The goal of this proposal is to develop a STAT palm-sized blood counter for monitoring complete blood counts (CBC) with 3-part differential during emergencies. Changes in blood counts can reflect acutely worsening medical conditions. For instance, a rapidly rising white blood cell count may occur during infections or a leukemic blast crises. Hematocrit values may rapidly decline in traumas, gastrointestinal bleeds, and post- procedure recoveries. Platelet values may drop significantly during chemotherapy and idiopathic thrombocytopenic purpura. During these situations, close and frequent monitoring of a patient's blood counts is a must to deliver the best care and treatment, whether it be blood transfusions, platelet transfusions, or drug administrations. These clinical scenarios reflect a significant market need. In 2007, $2.7 billion of hematology tests were performed. Of these, an estimated 25-35% of these tests were STAT tests, which are ideally performed at the point-of-care. The proposed blood counter samples a fingerstick of blood from the patient and analyzes it in real-time at the patient's side for point-of-emergency clinical decision making. This is in contrast to today's measurement technologies, which require a benchtop instrument and a trained technician. The central hypothesis for this Phase II SBIR effort is this: microfluidic technology can be utilized to develop an integrated palm-sized blood counter that requires only a pinprick of blood. The proposed 24-month Phase II effort leverages our Phase I accomplishments in microfluidics, sensitive detection, and precision measurements to develop a prototype handheld emergency blood sensor. Advances in detection and microfluidics are required to develop such a device. Specific Aim 1 will utilize our microfluidics technology to assess serial cell dilution ad red cell lysis. Specific Aim 2 will be utilized to develop an integrated optical and electrical impedance detection system required for measurement of a wide range of cell parameters. Specific Aim 3 will be utilized to develop a handheld, breadboard prototype of our STAT blood counter and validate its performance against a gold-standard blood counter across a set of clinical samples. Success in Phase II will lead to a Phase III effort which will include detailed product engineering for a commercial STAT blood counter product, tests for FDA 510(k) approval, and commercialization. The resulting product can be utilized in a wide- range of settings including ambulances, inpatient rooms, operating rooms, medical offices, and resource- starved settings.